1. Field of the Invention
This invention relates to electrical cable used to supply power to downhole equipment like submersible pumps in subterranean wells. More particularly, the invention relates to electrical cable encased in steel tubing that is known in the industry as reeled or coiled tubing. Optionally, the invention relates to reeled tubing that encases cable bundles comprising both electrical conductors and small-diameter tubing adapted to deliver lubricants, corrosion inhibitors or other fluids to downhole equipment.
2. Prior Art
It is well known that conventional electrical conductors comprising insulated copper wire lack sufficient tensile strength to support their own weight when used in the long vertical run lengths frequently needed for downhole applications. One method previously used to strengthen such conductors has been the incorporation of one or more steel cables inside the cable bundle.
Longitudinally wrapped and seamed cables comprising coaxial electrical conductors are disclosed in U.S. Pat. Nos. 3,394,400; 3,405,228; 3,530,019 and 4,083,484. Such cables are not, however, satisfactory for use in the vertical oilfield applications discussed above.
U.S. Pat. No. 3,615,977 discloses a method for insulating coaxial tubing systems using a material that is foamed in situ.
U.S. Pat. Re. No. 28,961 discloses a method and apparatus for manufacturing soft metal sheaths for electrical wires.
U.S. Pat. No. 4,938,060 discloses a method and apparatus wherein an electrical cable connected to a downhole sensor extends longitudinally up the interior of coil tubing to receiving and control equipment located at the surface adjacent the wellbore. The tubing conducts injection fluid to a desired location within the borehole and protects the electrical cable when running into or out of the hole. In this apparatus the coil tubing does not function to support the weight of the electrical cable.